Radio frequency amplifier with stable operation and restrained oscillation at low frequencies

Abstract

In a radio frequency amplifier, a resistor and an inductor are connected to a gate terminal of transistor such as an FET. Another resistor for preventing oscillation is connected to the inductor. A capacitor and a third resistor connected to each other in parallel are connected to the first resistor while the other ends thereof are grounded. A resistance value of the resistor for preventing oscillation is in the range of about 30 OMEGA to about 70 OMEGA . An inductance value of the inductor is such that an impedance value for a low frequency becomes negligibly small.

What is claimed is: 
     
       1. A radio frequency amplifier comprising: a transistor;   an inductor connected to an input terminal of the transistor;   a first resistor connected to the inductor;   a capacitor having one end connected to the first resistor and an other end grounded; and   a second resistor connected between a power supply terminal and the input terminal of the transistor.   
     
     
       2. A radio frequency amplifier comprising: a transistor;   a microstrip line connected to an input terminal of the transistor;   a first resistor connected to the microstrip line;   a capacitor having one end connected to the first resistor and an other end grounded; and   a second resistor connected between a power supply terminal and the input terminal of the transistor.   
     
     
       3. A radio frequency amplifier comprising: a transistor;   an inductor connected to an input terminal of the transistor;   a first resistor connected to the inductor;   a second resistor connected between a power supply terminal and the input terminal of the transistor; and   a capacitor and a third resistor connected to each other in parallel, each having one end connected to the first resistor and an other end grounded.   
     
     
       4. A radio frequency amplifier comprising: a transistor;   a microstrip line connected to an input terminal of the transistor;   a first resistor connected to the microstrip line;   a second resistor connected between a power supply terminal and the input terminal of the transistor; and   a capacitor and a third resistor connected to each other in parallel, each having one end connected to the first resistor and an other end grounded.   
     
     
       5. A radio frequency amplifier according to claim 1, wherein a resistance value of the first resistor is in a range of about 30 Ω to about 70 Ω. 
     
     
       6. A radio frequency amplifier according to claim 2, wherein a resistance value of the first resistor is in a range of about 30 Ω to about 70 Ω. 
     
     
       7. A radio frequency amplifier according to claim 3, wherein a resistance value of the first resistor is in a range of about 30 Ω to about 70 Ω. 
     
     
       8. A radio frequency amplifier according to claim 4, wherein a resistance value of the first resistor is in a range of about 30 Ω to about 70 Ω. 
     
     
       9. A radio frequency amplifier according to claim 1, wherein an inductance value of the inductor is such that an impedance value for a low frequency becomes negligibly small. 
     
     
       10. A radio frequency amplifier according to claim 3, wherein an inductance value of the inductor is such that an impedance value for a low frequency becomes negligibly small. 
     
     
       11. A radio frequency amplifier according to claim 2, wherein a length of the microstrip line is such that an impedance value for a low frequency becomes negligibly small. 
     
     
       12. A radio frequency amplifier according to claim 4, wherein a length of the microstrip line is such that an impedance value for a low frequency becomes negligibly small. 
     
     
       13. A radio frequency amplifier according to claim 1, wherein an inductance value L of the inductor is set so as to satisfy a relation: about 10 Ω≦2 πfL≦about 100 Ω for an operating frequency f. 
     
     
       14. A radio frequency amplifier according to claim 3, wherein an inductance value L of the inductor is set so as to satisfy a relation: about 10 Ω≦2 πfL≦about 100 Ω for an operating frequency f. 
     
     
       15. A radio frequency amplifier according to claim 2, wherein a characteristic impedance of the microstrip line is set so as to be higher than a resistance value of the first resistor, and a length d of the microstrip line is set so as to satisfy a relation: λ/40≦d≦λ/8 for a wavelength λ of an operating frequency. 
     
     
       16. A radio frequency amplifier according to claim 4, wherein a characteristic impedance of the microstrip line is set so as to be higher than a resistance value of the first resistor, and a length d of the microstrip line is set so as to satisfy a relation: λ/40≦d≦λ/8 for a wavelength λ of an operating frequency. 
     
     
       17. A radio frequency amplifier according to claim 1, wherein the radio frequency amplifier is used in a microwave frequency band in a range of about 1 GHz to about 2 GHz, and an output power of the transistor is in a range of several hundreds of mW to several W. 
     
     
       18. A radio frequency amplifier according to claim 2, wherein the radio frequency amplifier is used in a microwave frequency band in a range of about 1 GHz to about 2 GHz, and an output power of the transistor is in a range of several hundreds of mW to several W. 
     
     
       19. A radio frequency amplifier according to claim 3, wherein the radio frequency amplifier is used in a microwave frequency band in a range of about 1 GHz to about 2 GHz, and an output power of the transistor is in a range of several hundreds of mW to several W. 
     
     
       20. A radio frequency amplifier according to claim 4, wherein the radio frequency amplifier is used in a microwave frequency band in a range of about 1 GHz to about 2 GHz, and an output power of the transistor is in a range of several hundreds of mW to several W. 
     
     
       21. A radio frequency amplifier according to claim 1, further comprising a third resistor having one end connected to the input terminal of the transistor and an other end grounded. 
     
     
       22. A radio frequency amplifier according to claim 2, further comprising a third resistor having one end connected to the input terminal of the transistor and an other end grounded.